coresight: etm4x: Fix accesses to TRCSEQRSTEVR and TRCSEQSTR

The TRCSEQRSTEVR and TRCSEQSTR registers are not implemented if the
TRCIDR5.NUMSEQSTATE == 0. Skip accessing the registers in such cases.

Fixes: 2e1cdfe1 ("coresight-etm4x: Adding CoreSight ETM4x driver")
Signed-off-by: Junhao He <hejunhao3@huawei.com>
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230114091632.60095-1-hejunhao3@huawei.com